Polysiloxane-polyoxyalkylene block copolymers with different polyoxyalkylene blocks in the average molecule

ABSTRACT

Polysiloxane-polyoxyaikylene block copolymers, which are intended for the production of polyurethane foams, are prepared. The foams obtained have an improved, finer cell structure and the collapse of the foams is reduced. It is essential for the invention that a mixture of polyoxyalkylene groups is present in the polysiloxane-polyoxyalkylene block copolymers. Further particulars are laid down for selecting the different polyoxyalkylene groups with regard to the respective molecular weights and the ratio of polyoxyalkylene groups to one another.

This is a divisional application of Ser. No. 08/144,990, filed Oct. 29,1993, now pending.

FIELD OF THE INVENTION

The invention relates to polysiloxane-polyoxyalkylene block copolymerswith different polyoxyalkylene blocks in average molecule and to theiruse in the production of polyurethane foams.

BACKGROUND INFORMATION AND PRIOR ART

For producing polyurethane foams, polysiloxanepolyoxyalkylene blockcopolymers are added to the mixture of reaction products. Saidcopolymers enable a uniform pore structure to be formed and stabilizethe foam formed up to the end of the reaction. However, not allpolysiloxane-polyoxyalkylene block copolymers are suitable in the sameway. In order to be useful as polyurethane foam stabilizers, thepolyoxyalkylene and the polysiloxane blocks of the block copolymer mustbe present in a well-balanced ratio, the structure of the two blocksalso being of great importance. For the structure of an as effective aspossible foam stabilizer, there is a plurality of variables for thepolyoxyalkylene block as well as for the polysiloxane block.

The polyoxyalkylene block can be composed of different oxyalkyleneunits, particularly of oxyethylene, oxypropylene and oxybutylene units.The weight ratio of these units to one another, as well as the molecularweight of the polyoxyalkylene block can be varied. Of importance is alsothe end group of the polyoxyalkylene block, which can be reactive withrespect to the polyurethane formation (for example, OH group) or inert(for example, alkoxy group). The polyoxyalkylene block can be linked tothe polysiloxane block by a hydrolytically stable C-Si bond or by thehydrolytically less stable C-O-Si bond. Different polyoxyalkylene blockscan also be linked to the polysiloxane block.

The polysiloxane block can be varied with respect to the nature andproportion of the silicon units. The siloxane block can be linear orbranched and have different molecular weights. The polyoxyalkylene blockcan be linked terminally and/or laterally to the polysiloxane block.

Only to a certain extent can. the effectiveness of aPolysiloxane-polyoxyalkylene block copolymer as a foam stabilizer bepredicted. The expert is therefore required to test the possiblevariations largely empirically. In view of the large, practicallyindeterminable number of possible variations, the finding of specialvariation possibilities and of appropriate block copolymers represents aprogress-amassing and thus inventive effort.

Polysiloxane-polyoxyalkylene block copolymers, which have differentpolyoxyalkylene groups in the average molecule, have already beendescribed repeatedly. The following publications are named as beingrepresentative of the large number of appropriate publications:

German Patent 15 70 647: Chloropolysiloxanyl sulfates are reacted withmixtures of alkylene oxide adducts, which consist of

50 to 95 OH-equivalent percent of polyalkylene glycol monoethers, whichconsist of ethylene oxide and propylene oxide units and contain 40 to70% by weight of oxypropylene units and have a molecular weight of 1,000to 3,000 and the hydroxyl groups of which preferably are secondary, and

5 to 50 OH-equivalent percent of aikylene oxide adducts of polyhydrichydroxyl compounds with a molecular weight of 130 to 3,500, thepolyalkylene glycol components of which consist of ethylene oxide and/orpropylene oxide units and which have an OH equivalent weight up to 1,750and the hydroxyl groups of which preferably are secondary, thequantitative ratio being selected so that there are at most 1.4 andpreferably 1.05 to 1.2 OH-equivalents per acid equivalent of thechloropolysiloxanyl sulfate.

German Pat. 16 94 366: The polysiloxanepolyoxyalkylene block copolymersare used as foam stabilizers, the polysiloxane block of which has aknown structure, but the polyoxyalkylene block of which consists of

25 to 70% by weight of a polyoxyalkylene with an average molecularweight of 1,600 to 4,000 and an ethylene oxide content of 20 to 100% byweight, the remainder being propylene oxide and optionally higheralkylene oxides, and

30 to 75% by weight of a polyoxyalkylene with an average molecularweight of 400 to 1,200 and an ethylene oxide content of 65 to 100% byweight, the remainder being propylene oxide and optionally higheralkylene oxides.

German Offeniegungsschrift 25 41 865: The polysiloxanepolyoxyalkyleneblock copolymers are defined with respect to their polyoxyalkyleneblocks, so that the one polyoxyalkylene block has an average molecularweight of 900 to 1,300 and consists of 30 to 55% by weight of ethyleneoxide, the remainder being propylene oxide, and the otherpolyoxyalkylene block has an average molecular weight of 3,800 to 5,000and consists of 30 to 50% of ethylene oxide, the remainder beingpropylene oxide.

European Publication 0 275 563: The block copolymer, described in thispublished European patent application, comprises three differentpolyoxyalkylene blocks, namely one block, which contains 20 to 60% byweight of oxyethylene units with a molecular weight of 3,000 to 5,500, afurther block with 20 to 60% by weight of oxyethylene units and amolecular weight of 800 to 2,900 and a third block, which contains onlypolyoxypropylene units and has a molecular weight of 130 to 1,200.

OBJECT OF THE INVENTION

An object of the invention is polysiloxanepolyoxyalkylene blockcopolymer, the application properties of which are optimized further, aparticular effort being made to find a stabilizer of high activity,which permits flexible polyurethane foams of very good cell fineness tobe produced even in the lower density range.

SHORT DESCRIPTION OF THE INVENTION

This improvement in properties is found in thosepolysiloxane-polyoxyalkylene block copolymers which, pursuant to theinvention, correspond to the following general, average formula:##STR1## wherein R¹ is an alkyl group with 1 to 4 carbon atoms or aphenyl group, with the proviso that at least 90% of the R¹ groups aremethyl groups,

R² has the same meaning as the R¹ group or represents the -R⁴ _(x) O-R³group, wherein

R⁴ is a divalent alkylene group, which may also be branched,

x has a value of 0 or 1 and

R³ is a mixture of

at least one polyoxyalkylene group A with an average molecular weight of350 to 6,000, consisting of >90 to 100% by weight of oxyethylene unitsand 0 to <10% by weight of oxypropylene units,

(b) at least one polyoxyalkylene group B with an average molecularweight of 700 to 5,500, consisting of 30 to 90% by weight of oxyethyleneunits and 70 to 10% by weight of oxypropylene units, and, optionally

(c) one or several polyoxyalkylene group(s) C with an average molecularweight of 500 to 5,000, consisting of 0 to <30% by weight of oxyethyleneunits and 100 to >70% by weight of oxypropylene units,

with the proviso that

(1) there is at least one --R⁴ _(x) OR³ group in an average blockcopolymer,

(2) there are at least 3 polyoxyalkylene groups of different averagemolecular weight and/or different oxyethylene content in the averageblock copolymer, and

(3) if no polyoxyalkylene group C is present, the polyoxyalkylene groupA has an average molecular weight of not less than 700, and

(4) if polyoxyalkylene groups A and C are present, at least one of thesegroups has an average molecular weight of not less than 700,

(5) the ratio of polyoxyalkylene groups A : B: C (in mole %) is 5 to 60:10 to 95: 0 to 80, the sum of the mole percentages adding up to 100,

has a value of 0 to 10,

has a value of 10 to 100, when b=0, or

has a value of 3 to 70, when b>0 and ≦4, or

has a value of 3 to 30, when b>4.

Up to 20% by weight of the oxypropylene units in the polyoxyalkylenegroups B and C can be replaced in each case by oxybutylene units.

The R¹ group preferably is a methyl group.

The R.sup. 4 group preferably is a group having the formula --(CH₂)₂--or--(CH₂)₃ --.

Preferably, the R³ polyoxyalkylene groups correspond to the formula(C_(m) H_(2m) O--)_(n) R⁵, the subscripts n and m being selected so thatthe conditions with respect to the composition and the respectivemolecular weight of the different polyoxyalkylene groups are fulfilled,and R⁵ is a hydrogen group, an alkyl group with 1 to 4 carbon atoms, anacyl group or an --O--CO--NH--R⁶ group, wherein R⁶ is an alkyl groupwith 2 to 6 carbon atoms or an aryl group, preferably a phenyl group.The different oxyalkylene groups can be distributed randomly orblockwise.

The following are the preferred ranges for the polyoxyalkylene groups:

    ______________________________________                                        polyoxyalkylene group A:                                                      average molecular weight                                                                           350 to 2,000                                             oxyethylene content                                                                               95 to 100                                                 oxypropylene content                                                                             5 to 0                                                     polyoxyalkylene group B:                                                      average molecular weight                                                                         1,300 to 4,500                                             oxyethylene content                                                                              40 to 70                                                   oxypropylene content and                                                                         60 to 30                                                   optional oxybutylene content                                                  polyoxyalkylene group C:                                                      average molecular weight                                                                           800 to 2,500                                             oxyethylene content                                                                               0 to 20                                                   oxypropylene content and                                                                         100 to 80                                                  optional oxybutylene content                                                  ______________________________________                                    

There must be at least 3 polyoxyalkylene groups of different averagemolecular weight and/or different oxyethylene content in the averageblock copolymer. For the case that no polyoxyalkylene group C ispresent, this means that either at least 2 polyoxyalkylene groups A and1 polyoxyalkylene group B or at least 1 polyoxyalkylene group A and 2polyoxyalkylene groups B must be present, which must fall within thescope of the definitions (a) and (b) with respect to their averagemolecular weight and/or their oxyethylene content.

Moreover, conditions (3) and (4) apply, according to which

(3) the average molecular weight of the polyoxyalkylene group A must notbe less than 700 when no polyoxyalkylene group C is present, and

(4) the average molecular weight of at least one of these groups mustnot be less than 700 when polyoxyalkylene groups A and C are present.

The molecular weight conditions of the A, B and C groups are illustratedin the following Table:

    ______________________________________                                        Polyoxyalkylene                                                                             Molecular Weight Range of the Groups                            Groups Present                                                                              A        B            C                                         ______________________________________                                        A and B       700-6000 700-5500                                               A, B and C    700-6000 700-5500     500-5000                                  or            350-6000 700-5500     700-5000                                  ______________________________________                                    

The ratio of the polyoxyalkylene groups A : B : C (in mole percent) is 5to 60: 10 to 95: 0 to 80, the sum of the mole percentages having to addup to 100.

Preferably, the ratio of A : B : C is 5 to 40 : 20 to 40 to 75, the sumof the mole percentages having to add up to 100. Particularly preferredratio is 10 to 30: 20 to 40: 50 to 75, the mole percentages adding up to100.

The inventive block copolymers can be produced by known methods. If thePolyoxyalkylene block are linked by an SiC bond to the polysiloxanebackbone, polyoxyalkylene ethers of alcohols with an olefinic doublebond are added to an SiH group of a hydrogensiloxane in the presence ofhydrosilylation catalysts, particularly platinum catalysts. If thepolyoxyalkylene blocks are linked to the polysiloxane backbone by anSiOC bond, chloropolysiloxanyl sulfates are reacted with polyethermonools with neutralization of the mineral acid that is set free. It isalso possible to transesterify the appropriate alkoxysiloxanes withpolyether monools. Appropriate synthesis methods are described in theliterature cited above.

The inventive polysiloxane-polyoxyalkylene block copolymers haveoutstanding application properties and can also be used in combinationwith other stabilizers of the state of the art. The flexible foams,produced with these polymers as foam stabilizers, exhibit an excellentratio of cell fineness to stabilization.

They are used in the usual amounts of, for example, 0.3 to 2.5% byweight, based on the polyol, and preferably, of 0.8 to 1.5% by weight,for the preparation of polyurethane foams.

In the following Examples, the application properties of the inventivepolymers are explained in even greater detail, it being understood thatthese examples are provided by way of illustration and not by way oflimitation.

Example 1

Into a flask, equipped with stirrer, thermometer, gas inlet andstillhead, 37.2 g (=0.0188 moles) of a polyether having the averageformula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.40 (C.sub.3 H.sub.6 O--).sub.26 CH.sub.3 (Type A),

17.5 g (=0.0125 moles) of a polyether having the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.12 (C.sub.3 H.sub.6 O--).sub.14 H (Type B),

    367.5 g (=0.0938 moles) of a polyether having the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.42 (C.sub.3 H.sub.6 O--).sub.34 COCH.sub.3 (Type B)

and 500 mL of toluene are added. In order to dry the polyether mixtureazeotropically, 150 mL of toluene are distilled off under a nitrogenatmosphere. After that, the flask is provided with a reflux condenserand a dropping funnel and nitrogen continues to be passed through theapparatus. At a temperature of about 105° C., 0.3 g of a 10% solution ofH₂ PtCl₆.6H₂ in i-propanol are added and stirred in for 5 minutes. Now80.4 g (=0.1 moles of SiH) of a siloxane having the average formula

(CH₃)₃ SiO--[(CH₃)₂ SiO--]₅₈ [(CH₃)HSiO--]₆ Si(CH₃)₃

are added dropwise over a period of 20 minutes. The reaction is allowedto continue for 4 hours, when an SiH conversion of 99.1% is attained(determined by way of the hydrogen that can be split off in an alkalinemedium with n-butanol).

Example 2

Into a flask, equipped with dropping funnel stirrer, thermometer, gasinlet and reflux condenser, 7.5 g (=0.0125 moles) of a polyether havingthe average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.12 CH.sub.3 (Type A),

301.8 g (=0.075 moles) of a polyether having the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.45 (C.sub.3 H.sub.6 O--).sub.34 CH.sub.3 (Type B),

56.6 g (=0.0375 moles) of a polyether having the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.5 (C.sub.3 H.sub.6 O--).sub.21 CH.sub.3 (Type C)

and 16 mg of C₂ H₄.C₅ H₅ N.PtCl₂ are added. Nitrogen is passed throughthe apparatus. After the temperature is raised to 120° C., 65.5 g (=0.1moles of SiH) of a siloxane with the average formula

    H(CH.sub.3).sub.2 SiO--[(CH.sub.3).sub.2 SiO--].sub.80 [(CH.sub.3)HSiO--].sub.8 Si(CH.sub.3).sub.2 H

are added dropwise. The reaction is allowed to continue for 2.5 hoursThe SiH conversion is 99.4%.

Example 3

Into a flask, equipped with stirrer, thermometer, gas inlet and refluxcondenser, 18.7 g (=0.0188 moles) of a polyether having the averageformula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.21 CH.sub.3 (Type A),

35.0 g (=0.025 moles) of a polyether having the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.12 (C.sub.3 H.sub.6 O--).sub.14 H (Type B),

75.6 g (=0.25 moles) of a polyether having the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.46 (C.sub.3 H.sub.6 O--).sub.16 CH.sub.3 (Type B),

84.8 g (=0.0563 moles) of a polyether having the average formula

84.8 g (=0.0563 moles) of a polyether having the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.1 (C.sub.3 H.sub.6 O--).sub.24 CH.sub.3 (Type C)

and 87.7 g (=0.1 moles of SiH) of a siloxane formula

    (CH.sub.3).sub.3 Sio--[(CH.sub.3).sub.2 SiO--].sub.130 [(CH.sub.3)HSiO--].sub.12 Si(CH.sub.3).sub.3

are added and nitrogen is passed through the apparatus. After thetemperature is raised to 110° C., 12 mg of cis-[PtCl ₂ (NH₃)₂ ] areadded. After a slightly exothermic reaction, the batch becomes clear.The reaction is allowed to continue for 3.5 hours, after which the SiHconversion is 98.9%,

Example 4

Into a flask, equipped with stirrer, thermometer, gas inlet andstillhead, 23.2 g (=0.0385 moles) of a polyether having the averageformula

    C.sub.4 H.sub.9 O--(C.sub.2 H.sub.4 O--).sub.12 H (Type A),

22.0 g (=0.0055 moles) of a polyether having the average formula

    C.sub.4 H.sub.0 O--(C.sub.2 H.sub.4 O--).sub.82 (C.sub.3 H.sub.6 O--).sub.5.4 H (Type A),

198.2 g (=0.0661 moles) of a polyether having the average formula

    C.sub.4 H.sub.9 O--(--C.sub.2 H.sub.4 O--).sub.23 (C.sub.3 H.sub.6 O--).sub.33 H (Type B)

and 1,100 mL of toluene are added. Under a blanket of nitrogen, 150 mLof toluene are distilled off for the azeotropic drying of the polyethermixture. At 50° C., the stillhead is exchanged for a reflux condenser.Subsequently, 65.8 g (=0.1 moles of SiX) of a chloropolysiloxanylsulfate having the average formula ##STR2## are added. Ammonia gas isthen passed in at 60° C., until the contents of the flask reactammoniacallY. The reaction is allowed to continue for a further hourwhile ammonia gas is being passed in slowly. Subsequently, theprecipitated salt is filtered off. After that, the toluene is distilledoff at 70° C. and 20 mbar.

Example 5

Under the conditions of Example 1, 3.8 g (=0.0063 moles) of a polyetherhaving the average formula

    Ch.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.12 (CH.sub.3 (Type A),

12.4 g (=0.0063 moles) of a polyether having the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.40 (C.sub.3 H.sub.6 O--).sub.2.6 CH.sub.3 (Type A),

46.0 g (=0.0313 moles) of a polyether having the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.16 (C.sub.3 H.sub.6 O--).sub.12 CH.sub.3 (Type B),

75.2 g (=0.0188 moles) of a polyether having the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.45 (C.sub.3 H.sub.6 O--).sub.34 H (Type B)

and 94.4 g (=0.0625 moles) of a polyether having the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.5 (C.sub.3 H.sub.6 O--).sub.21 CH.sub.3 (Type C)

are reacted with 87.7 g (=0.1 moles of SiH) of a siloxane with theaverage formula

    (CH.sub.3).sub.3 SiO--[(CH.sub.3).sub.2 SiO--].sub.130 [(CH.sub.3)HSiO--].sub.6 Si(CH.sub.3).sub.3

with addition of 400 mL of toluene (of which 150 mL are used forazeotropic drying) in the presence of 0.18 g of a 10% solution of H₂PtCl₆.6H₂ O in i-propanol. An SiH conversion of 98.5% is achieved.

Example 6

(not of the invention)

Under the conditions of Example 1, 27.5 g (=0.0438 moles) of a polyetherhaving the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 O--(C.sub.2 H.sub.2 H.sub.4 O--).sub.23 (C.sub.3 H.sub.6 O--).sub.8 CH.sub.3 (Type B),

and 327.0 g (=0. 0813 moles) of a polyether having the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.45 (C.sub.3 H.sub.6 O--).sub.34 CH.sub.3 (Type B)

are reacted with 80.4 g (=0.1 moles of SiH) of a siloxane having theaverage formula

    (CH.sub.3).sub.3 SiO--[(CH.sub.3).sub.2 SiO--].sub.58 [(CH.sub.3)HSiO--].sub.6 Si(CH.sub.3).sub.3

with addition of 450 mL of toluene (of which 150 mL are used forazeotropic drying) in the presence of 0.25 g of a 10% solution of H₂PtC1₆.6H₂ O in i-propanol. An SiH conversion of 98.8% is achieved.

Example 7

(not of the invention)

Under the conditions of Example 1, 19.4 g (=0.0125 moles) of a polyetherhaving the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.23 (C.sub.3 H.sub.6 O--).sub.8 CH.sub.3 (Type B),

73.6 g (=0.05 moles) of a polyether having the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.16 (C.sub.3 H.sub.6 O--).sub.12 CH.sub.3 (Type B)

75.5 g (=0.05 moles) of a polyether having the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.2 H.sub.4 O--).sub.5 (C.sub.3 H.sub.6 O--).sub.21 CH.sub.3 (Type C)

and 32.1 g (=0.0125 moles) of a polyether having the average formula

    CH.sub.2 ═CH--CH.sub.2 O--(C.sub.3 H.sub.6 O--).sub.43 CH.sub.3 (Type C)

are reacted with 87.7 g (=0.1 moles of SiH) of a siloxane having theaverage formula

    (CH.sub.3).sub.3 SiO--[(CH.sub.3).sub.2 SiO--].sub.130 [(CH.sub.3)HSiO--].sub.12 Si(CH.sub.3).sub.3

with addition of 400 mL of toluene (of which 150 mL are used forazeotropic drying) in the presence of 0.2 g of a 10% solution of H₂PtCl₆.6H₂ O in i-propanol. An SiH conversion of 98.4% is achieved.

The application of the foam stabilizers produced was tested with a foamformulation in the following manner:

In each case, 300 parts of a conventional, commercial polyether for thepreparation of flexible urethanes, which has three hydroxyl groups in anaverage molecule and a molecular weight of 3,500, are mixed with goodstirring with 15 parts of water, 30 parts of a physical blowing agent,the appropriate amount of the foam stabilizer to be tested, 0.33 partsof diethylenetriamine and 0.6 parts of tin octoate. After the additionof 125 parts of toluene diisocyanate (2,4 and 2,6 isomers mixture in theratio of 4 : 1), stirring is continued with a smooth stirrer for 7seconds at 3000 rpm and the mixture is poured into a box. A foam with afine pore structure is formed, on which the following data are measured:

1. The collapse of the foam at the end of the rising phase (given in theTable below as "collapse").

2. The number of cells per centimeter of foam is counted under amicroscope.

In the following Table, three values are given in each case for threedifferent concentrations in the ratio of 1.8 : 1.3 : 1.0 for inventivestabilizers (Examples 1 to 5) as well as for stabilizers not of theinvention (Examples 6 and 7).

    ______________________________________                                        Example       Collapse  Cells per cm                                          ______________________________________                                        1             0.4/0.7/1.1                                                                             13/12/12                                              2             1.0/1.2/1.6                                                                             15/14/14                                              3             0.7/0.9/1.2                                                                             15/15/14                                              4             1.1/1.3/1.6                                                                             12/12/12                                              5             0.3/0.7/0.9                                                                             15/14/14                                              6             0.2/0.3/1.9                                                                             06/05/04                                              7             2.1/2.5/3.3                                                                             16/15/13                                              ______________________________________                                    

Through the use of the inventive block copolymers as active foamstabilizers for the production of polyurethane foams, it is thuspossible to obtain foams with a cell structure, which is distinctlyfiner than that of foams of the state of the art. At the same time, thecollapse is slight.

We claim:
 1. A polysiloxane-polyoxyalkylene block copolymer havingdifferent polyoxyaikylene blocks in an average molecule, comprising thegeneral formula ##STR3## wherein R¹ is an alkyl group with 1 to 4 carbonatoms or a phenyl group, with the proviso that at least 90% of the R¹groups are methyl groups,R² has the same meaning as the R¹ group orrepresents the --R⁴ _(x) O--R³ group, wherein R⁴ is a divalent alkylenegroup, with or without branches, X has a value of 0 or 1, and R³ is amixture of(a) at least one polyoxyalkylene group A with an averagemolecular weight of 350 to 6,000, consisting of >90 to 100% by weight ofoxyethylene units and 0 to <10% by weight of oxypropylene units, and (b)at least one polyoxyalkylene group B with an average molecular weight of700 to 5,500, consisting of 30 to 90% by weight of oxyethylene units and70 to 10% by weight of oxypropylene units,with the proviso that (1)there is at least one --R⁴ _(x) OR³ group in the average blockcopolymer, (2) there are at least 3 polyoxyalkylene groups of differentmolecular weight, or different oxyethylene content or both in theaverage block copolymer, (3) the polyoxyalkylene group A has an averagemolecular weight of not less than 700, and (5) the ratio ofpolyoxyalkylene groups A: B (in mole %) is 5 to 60 : 10 to 95 the sum ofthe mole percentages adding up to 100, b has a value of 0 to 10, has avalue of 10 to 100, when b=0, or has a value of 3 to 70, when b>0 and≦4, or has a value of 3 to 30, when b>4.
 2. The block copolymer of claim1, further comprising that R³ mixture also contains one or severalpoloxyalkylene groups C having an average molecular weight of 500 to5,000, consisting of 0 to <30% by weight of oxyethylene units and 100to >70% by weight of oxypropylene units, with the further proviso thatat least one of groups A and C has an average molecular weight of notless than 700, and the ratio of polyoxyalkylene groups A: B: C (in mole%) is 5 to 60 : 10 to 95 : 0 to 80, the sum of the mole percentagesadding up to
 100. 3. The block copolymer of claim 2, comprising that upto 20% by weight of the oxypropylene units can in each case be replacedby oxybutylene units in the polyoxyalkylene groups B and C.
 4. The blockcopolymer of claims 2 or 3, comprising that the ratio of thepolyoxyalkylene groups A: B: C (in mole percent) is 5 to 40: 20 to 60:40 to 75, the sum of the percentages having to add up to 100 molepercent.
 5. The block copolymer of claims 2 or 3, comprising that theratio of the polyoxyalkylene groups A: B: C (in mole percent) is 10 to30 : 20 to 40 : 50 to 75, the sum of the percentages having to add up to100 mole percent.
 6. The block copolymer of claim 2 or 3, comprisingthat the polyoxyalkylene groups A, B and C correspond to the formula(C_(m) H_(2m) O--)_(nR) ⁵, subscripts n and m being selected so that theconditions with respect to the composition and the respective molecularweight of the different polyoxyalkylene groups are fulfilled, and R⁵being a hydrogen group, an alkyl group with 1 to 4 carbon atoms, an acylgroup or an --O--CO--NH--R⁶ group, wherein R⁶ is an alkyl group with 2to 6 carbon atoms or an aryl group.